Retard air control for stokers



June 28, 1938. F. w. STUART RETARD AIR CONTROL FOR STOKERS Filed Oct.13, 1936 2 Sheets-Sheet l INVENTOR. F760 #4 Szzmrf WW: 7 v

ATTORNEYS June 28, 1938. F. w. STUART RETARD AIR CONTROL FOR STOKERSFiled Oct. 13, 1936 2 Sheets-Sheet 2 INVENTOR. fiGQ 511107? BY W WATTORNEY5 ill) Patented June 28, 1938 STTES The present inventionrelates to a means for automatically controlling the volume of airdelivered from a fan driven by a constant speed motor and specificallyto a device for restricting the amount of air delivery of a constantspeed fan to a gore-determined minimum during the initial operationthereof and which gradually permits the delivery of air at the maximumfan volume.

My invention is particularly adapted for use in conjunction withautomatic coal burning stoker equipment employing a fan for the deliveryof air to the retort thereof. object of my invention is to provide adevice which will materially reduce the amount of fly ash discharged bythe heating machine thereby diminishing fly ash deposit on the heatingsurfaces of the furnace which is conducive to the eidcient operation ofthe unit, whilst also lessening the danger of the fly ash escaping intothe air through the flue pipe and-chimney, thus in= creasing thepersonal health factor in stoker usage.

Another object of the invention is to provide a means whereby themaximum amount of air delivery from a stoker fan, during stokeractivity, may be periodically decreased, thus allowing a greater-volumeof air to be used-for combustion which permits a more intense firewithout the consequent thinning of the fuel bed.

A further object of the invention is to provide lowing specification anddrawings which disclose the preferred embodiment of my invention, and

in which:

Fig. 1 is a cross sectional view of my device positioned upon the airconduit of a stoker unit.

Fig. 2 is a front elevational view of the stoker unit with the devicedisposed thereon.

, Fig. 3 is a front elevational view of a stoker unit showing a modifiedform of my device.

v Fig. 4 is a wiring diagram used in conjunction with my device.

Generally, my device consists of a shutter interposed either in the airduct -of a stoker unit between the fan and the retort or over the airinlet of the fan thereof, and which is adapted to be moved to open orclose said air conduit or inlet In this connection, an

by means of a heat responsive expansion element, connected thereto bysuitable linkage. Associated with or adjacent this element is positionedan electrically operated heating coil which is wired in parallel withthe stoker motor and fan motor circuits. The shutter is devised to benormally in a position to close the air conduit or fan inlet so thatupon actuation of the motor, the heating coils will be energized tooperate the expansion element, thus gradually moving the shutter to aposition to open the air conduit or fan inlet.

The exhausted time of shutter'movement may be varied by means of an airescapement valve adapted to control the movement of air between theheating coil and the expansion element. A switch is placed in series inthe heating coil circult which is adapted to break the circuit when themarlzimum movement of the expansion element has been reached and whichcloses the circuit at an intermediate position of the expansion element.

Specifically, my device ii as shown in Fig. 2, is positioned upon theair conduit i of a stoker unit 18 between the fan and the retort ill.The fan is driven in the conventional manner by a con= stant speed motorii, the latter usually being employed to drive the coal feed screw oithe stoker. The device comprises a base casting i2 (Fig. 1) having acentrally disposed aperture iii and an ofiset portion i l. The oppositeends of the casting are provided with lateral grooves 25 adapted toreceive straps it which are drawn over the casting and are fastened tothe air conduit by bolts ii to permanently fasten the casting thereon. Asleeve casing it is positioned in a circular inset portion it of thebase and encloses a porcelain coil mounting 2d. The coil mounting has arelatively large centrally disposed annular opening it, the verticalwall thereof being provided with a spiral groove 22 to receive anelectric heating element or resistance 23. I

The terminals 24 and 25 of the coil are led through horizontal holes 26in the mounting and are secured to circuit contacts 271. These conswitch are closed. Thus.

flanges I! having holes. ll therein being adapted to receive elongatedbolts 31 to permanently secure the cap and the casing to the base. Anexpansion element which conveniently takes the form of a metallicbellows 38 containing a volatile liquid or gas is disposed centrally ofthe coil mounting and adlacent the resistance coil. A threaded lug l8integral with the bellows extends from the top central surface thereofand is received in a centrally disposed aperture 40 in the cap, a boltll being provided to engage the threaded portion of the lug and fastenthe bellows permanently to the cap. The lower free end of the bellowshas a projection l2 secured thereto by means of a screw ll, whichextends through the central aperture II in the base and into the airconduit proper.

A valve or shutter 44 is interposed in the air conduit 1 and issubstantially the same size as the transverse inside dimensions of saidconduit there being provided a small air escapement 45 about the shutterand the conduit walls. The shutter is normally in vertical orclosed-position and is pivoted on a transverse shaft 4! fastened to thevertical walls of the conduit. The expansion or contraction of thebellows is devised to open and close the shutter and to this end a lever41 is provided which has for its fulcrum a pin 48 held in a bracket 49,the latter being fastened to the bottom surface of the base by bolt IO.One end of the lever has an elongated slot 8i therein to receive apintle 52 secured in a circular arm ll fastened to the shutter adjacentthe upper end thereof. Intermediate the fulcrum and the arm engaging endof the lever and ad- Jacent the fulcrum, the projection II is fastenedto thelever by a pin ll. The free end of the lever has fastened thereonby means of spring clips II, a mercury tube switch 5!, which is normallheld in a position to close its contacts II and I.

Thelead wires l9 and 60 are led to the contact plate 28 and are wiredthereto in the following manner. Referring to Fig. 4, current isintroduced to the constant speed motor Ii of the stoker unit by wires BIand If, the said circuit being controlled by the conventionalthermostat. The heat producing resistance coil is wired in parallel tothe motor circuit by wires 83 and N, the mercury tube switch contacts I!and ll being placed in series in the resistance coil circuit.

In operation therefore, (Figs. 1 and 4) when the constant speed motorfor driving the fan and incidently, the feedscrew of the stoker unit isinoperative, the shutter 44 will remain in its normal or closedposition. when the current is supplied to the fan actuating motor, itsmaximum volume of air will be forced through the air conduit to theretort in the direction of the arrow, the shutter serving to retard theair thus allowing a minimum amount of said air to reach the retort. Acurrent will also be sent to the heat producing resistance coil II andbecause it is in normal lever position, the contacts of the mercury aminimum amount of air is delivered to the tuyere which is not ofsufficient velocity to discharge the accumulation of ily ash therein,but allows the fire to reduce this ash to a .cinder formation.

As has been said, the resistance coil is energised when current issupplied to the motor. The coil therefore gradually raises thetemperature of the air about the expansion element thus causing themovement of the free end thereof to move the lever and its associatedparts, to bring them into a position indicated by the dotted lines 85,whereby the shutter is in open position thus permitting a maximum volumeof air to be delivered to the tuyere.

To regulate the elapsed time of shutter movement which is dependent uponthe rate of expansion of the expansion element it is necessary to permitthe escape of heat set up by the resistance coils. To this end. Iprovide a sleeve 65 rotatably mounted inside the cap 33 which has anumber of perforations 61 to register with a number of holes 88 formedin the cap. This construction results in an air escapement valve whichmay be regulated by rotating the sleeve to open or close the openings.Forced air from the conduitis therefore admitted through aperture l3 tobe passed about the expansion element and discharged through theseescapement valves. By adjustment of the valves, it will be seen that theeffectiveness of the radiant heatof the coil upon the expansion of theexpansion element may be varied to control the elapsed time of shuttermovement.

when the lever has reached the maximum or open shutter position, thecontact in the mercury switch is devised to be broken, thus interruptingthe current flow to the heating coil. The subse quent cooling of theheating coil and the expansion element allows the latter to contract,and by action of the lever allows the shutter to decrease the conduitopening. When the shutter closes to 'a point intermediate its open orclosed position, the mercury switch contacts are devised to-again closethe heating coil circuit to again expand the expansion element and openthe shutter. This cycle of operation continues so long as the fandriving motor is actuated. The last mentioned operation is devised toperiodically decrease the maximum volume of fan delivery to allow agreat:

er amount of air to be used for combustion which permits a more intensefire without the consequent thinning of the fuel bed as will readily beunderstood. The shutter will return to its normal closed position whenthe fan is inoperative.

A modification of the application of my device is shown in Fig. 3. Thedevice 6 is constructed similar to the preferred form except that thelever 41 is pivoted to a substantially U-shaped arm ll which is fastenedto the transverse shaft 48. The extended portion of the shaft is securedto an arm 69 which is rotatably fastened to a link 'Il,.the free end ofthe latter being pivoted to an arm H which regulates the rotary movementof a shutter 12. The shutter is mounted for rotation about the intakeopenings 13 of the fan II by means of a bolted flange 15. The shutter isprovided with a number of openlugs-1' which register with the opening 12when the expansion element is in maximum expanded condition.

In this way, the amount of air delivered through the air duct 1 may beregulated by my device 8 in a manner similar to that used in mypreferred form.-

Whatisclaimed is: y

1. In a retard air control for stokers the combination of a constantspeed motor, a fan driven by the motor, a circuit for said motor, a heatproducing electrical resistance wired in parallel with the circuit,'aheat responsive, expansion element adjacent the resistance, means forvarying the rate of movement of the expansion element, an air conduitfor the fan, a shutter, pivotally interposed in the air conduit, meansassociated with the expansion element and the shutter to open and closesaid shutter and comprising a lever having a fulcrum disposedsubstantially centrally thereof, an arm positioned on the shutter andpivotally engaging an end of the lever, and means for connecting theexpansion element to the lever intermediate the fulcrum and the armconnecting means, and a switch in series in the resistance circuit andassociated with the lever, said switch being adapted to break theresistance circuit when the shutter is open and to energize saidresistance circuit when the shutter is in an intermediate or closedposition.

2. In a retard air control for stokers the combination of a constantspeed motor, a fan driven by the motor, a circuit for said motor, an airconduit for the fan, a heat producing, electrical resistance wired inparallel with the circuit, a heat responsive expansion element adjacentthe resistance, a casing for the resistance and the expansion element, acap for the casing, means for introducing air from the air conduit tothe interior of the casing, a plurality of adjustable openings in thecap to allow the escapement of air from the casing, a movable shutterinterposed in the air conduit, means associated with the expansionelement and the shutter to open and close said shutter, and a switch inseries in the resistance circuit and adapted to break the resistancecircuit when the shutter is open and to energize said resistance circuitwhen the shutter is in an.

intermediate or closed position. a I

-3. In a retard air control for stokers the combination of a constantspeed motor, a fan driven by the motor, a circuit for said motor, an airconduit for the fan, a heat producing, electrical resistance wired inparallel with thecircuit, a heat responsive expansion element adjacentthe resistance, a casing for the resistance and the expansion element, acap for the casing, means for introducing air from the air conduit tothe interior of the casing, a plurality of adjustable openings in thecap to allow the escapement of air from the casing, a shutter pivotallyinterposed in the air conduit, means associated with the expansionelement and the shutter to open and close said shutter and comprising alever having a fulcrum disposed substantially centrally thereof, an armpositioned on the shutter and pivotally engaging an end of the lever andmeans for connecting the expansion element to the lever in j termediatethe fulcrum and the arm connecting -means, and a switch in series in theresistance circuit and associated with the lever, said switch beingadapted to break the resistance circuit when the shutter is open and toenergize said resistance circuit when the shutter is in an intermediateor closed position.

4. In a retard air control for stokers the combination of a constantspeed motor, a fan driven by the motor, a circuit for said motor, an airinlet opening for the fan, a heat producing electrical resistance wiredin parallel with the circuit, a heat responsive, expansion elementadjacent the resistance, a casing for the resistance and the expansionelement, a cap for the casing, means for introducing air from the airconduit to the interior of the casing, a plurality of adjustableopenings in the cap to allow the escapement of air from the casing, ashutter movably positioned over the inlet opening of the fan, meansassociated with the expansion element and the shutter to open and closethe inlet openings by the shutter and comprising a lever having a.fulcrum disposed substantially centrally thereof, a shaft, an

arm positioned on the shaft and pivotally engaging an end of the leverand linkage connecting the shaft to the shutter, and means forconnecting the expansion element to the lever interme- 5. In a retardair control for stokers the combination of a retort, a constant speedmotor, a circuit for the motor, a fan driven by the motor, an airconduit interposed between the fan and the retort, means actuated by themotor for supplying fuel to'the retort, a valve in the air conduit, andmeans wired in parallel with the motor circuit for gradually openingsaid valve when the motor is initially actuated.

6. In a retard air control for stokers, the combination of a constantspeed motor, a retort, a fan driven by said motor, an air conduitinterposed between the fan and the retort, means actuated by the motorfor supplying fuel to the 7. In a retard air control for stokers, thecombination of a constant speed motor, a retort, a fan driven by saidmotor,an air conduit interposed between the !an and the retort, meansactuated by the motor for supplying fuel to the retort, a circuit forthe motor, a heat producing electrical resistance wired in parallel withthe circuit, a heat responsive expansion element adjacent theresistance, means for varying the rate of movement of the expansionelement, a valve in the air conduit and means associating the movementof the expansion element with the valve for the gradual opening of saidvalve during initial actuation of the motor.

8. In a retard air control for stokers, the combination of a retort, aconstant speed motor, a

i'an driven by said motor, an air conduit interfan driven by said motor,an air conduit interposedbetween the fan and the retort, means actuatedby the motor for supplying fuel to the retort, a circuit for the motor,a. heat producing, electrical resistance wired in parallel with thecircuit, a heat responsive expansion element adjacent the resistance, a.valvein the air conduit, means associating the movement of the expansionelement with the valve to gradually open said valve and a switch wiredin series in the resistance circuit and associated with the movement ofthe valve to break the resistance circuit when the valve is open and .toenergize said circuit when the valve is in an intermediate or closedposition.

FRED W. STUART.

